Method of manufacturing security elements for electronic article surveillance and security element

ABSTRACT

The invention is directed to a method of manufacturing security elements ( 1 ) for electronic article surveillance, said security elements ( 1 ) being made of at least two layers ( 2, 3 ), and to a security element ( 1 ) manufactured according to the method of the invention.  
     The object underlying the invention is to propose a method of manufacturing low cost and reliably operating security elements ( 1 ).  
     The method of the invention comprises the steps of applying a first layer ( 2 ) of a cellulose material ( 6 ) in the still moist state to a second layer ( 3 ). of a cellulose material ( 5 ), with soft magnetic elements ( 4 ) which emit a characteristic signal in the interrogating field of an article surveillance system being added to one of the two layers ( 2; 3 ); and subsequently die stamping or cutting out the desired shape of the security elements ( 1 ) from the two layers ( 2, 3 ) in the dry state.

[0001] This invention relates to a method of manufacturing security elements for electronic article surveillance, said method comprising the step of making the security elements of at least two layers. The present invention also relates to a security element manufactured according to the method of this invention.

[0002] From EP 0 340 034 B1 there is known a security element for electronic article surveillance in warehouses and department stores which contains fibers of a material displaying high permeability and low coercive force. Either these fibers are contained in a paper substrate or they are affixed to the substrate by adhesive bonding. The orientation of the fibers in or on the substrate is completely arbitrary, as the result of which, there is a relatively high probability of the fibers overlapping with other fibers and coupling with them magnetically. The magnetic flux of the fibers is thereby concentrated and intensified, making it possible for the security elements described in the patent specification to be detected regardless of their orientation in relation to the interrogating field of the electronic article surveillance system.

[0003] It is an object of the present invention to propose a method for the manufacture of low cost and reliably operating security elements for electronic article surveillance.

[0004] This object is accomplished in that a first layer of a cellulose material is applied in the still moist state to a second layer of a cellulose material, with soft magnetic elements, which emit a characteristic signal in the interrogating field of an article surveillance system, being added to one of the two layers, and in that the desired shape of the security elements is die stamped or cut out of the two layers in the dry state.

[0005] The advantage of the method of the present invention is to be seen mainly in the possibility for the layer with the soft magnetic fibers to be very thin because it is supported by the second thicker layer. Hence the layer with the soft magnetic fibers can be made of a highly dilute paper fiber suspension, which-as is described below in further detail-affords immense advantages a s regards the subsequent orientation of the soft magnetic fibers and their processible length in the still moist cellulose material of the second layer. Furthermore, with both layers being applied to each other in the still moist state, they adhere firmly together after drying without the need of any additional steps, e.g., adhesive bonding the two layers.

[0006] According to a preferred further aspect of the method of the present invention, provision is made for the soft magnetic elements, which are fibers of very small diameter, to be oriented in essentially longitudinal direction of the material web by external force applied when the fibers are in the moist state. In accordance with a particularly favorable embodiment of the method, this orientation is performed by providing a device, either above or underneath the layer of cellulose material containing the soft magnetic fibers, which produces a magnetic field in longitudinal direction, meaning in the running direction of the material web. Because at this instant the cellulose material is in a still moist state, the fibers are oriented in the running direction of the material web under the action of the magnetic field. Alternatively, an orientation of the fibers in the running direction of the material web can also be effected forcibly by accelerating the layer of cellulose material with the integrated soft magnetic fibers; this results likewise in the fibers being oriented in the longitudinal direction of the layer.

[0007] The security element for electronic article surveillance produced by this method incorporates the following features: The first layer is a cellulose material comprised of cellulose fibers. The second layer is comprised likewise of a cellulose material made up of a mixture of cellulose fibers and soft magnetic elements. These soft magnetic elements are excited-as was mentioned several times already-in a magnetic interrogating field of an electronic article surveillance system to emit a characteristic signal.

[0008] As previously explained in connection with the method of the present invention, the magnetic elements are fibers made of a soft magnetic material. With a view to achieving as high a detection rate as possible it has proven advantageous for the length of the soft magnetic fibers to exceed 2 cm on average.

[0009] A preferred further aspect of the security element of the present invention provides for the cellulose material of the second layer to contain no more than half as many soft magnetic fibers as cellulose fibers. The superposed arrangement of two layers of cellulose material as disclosed in the invention permits in particular the concentration of cellulose fibers contained in the layer with the soft magnetic fibers to be maintained at a very low level without detracting from stability. On account of the extremely dilute fiber suspension for the second layer this preferred embodiment of the security element of the present invention allows

[0010] (a) relatively long magnetic fibers to be admixed to the cellulose material;

[0011] (b) the magnetic fibers to disperse well without excessive bending; and

[0012] (c) the magnetic fibers to be easily oriented by the application of external forces if required.

[0013] The present invention will be described in more detail in the following with reference to the accompanying drawing. In the drawing,

[0014]FIG. 1 is a schematic illustration of a device used for implementing the method of the present invention; and

[0015]FIG. 2 is a perspective view of a security element manufactured in accordance with the method of the present invention.

[0016]FIG. 1 is a schematic representation of a device used for implementing the method of the present invention. The cellulose material 6 is placed on a support surface 10 through a delivery device 8. The support surface 10 is, for example, a fine-meshed endless net, which is guided over reversing rollers 14, 15. Excess water can be removed from the cellulose material 6 through the mesh of the net 10.

[0017] A second amount of cellulose material 5 is placed on a second support surface 9 by means of a further delivery device 7. This support surface 9 can also be a fine-meshed endless net, which is guided over reversing rollers 11, 12, 16. Underneath the reversing roller 16 the layer 3 of cellulose material 5 is applied, while still moist, to the first layer 2 of cellulose material 6. The direction of travel of the web of material composed of the layers 2, 3 is indicated by an arrow in the drawings.

[0018] While the cellulose material 6 of the first layer 2 consists of cellulose fibers only, soft magnetic fibers 4 are mixed into the cellulose material 5 of the second layer 3. The mixing ratio is maximally 50:50. A device 14, which generates a magnetic field in the running direction of the web of material 2, 3 is arranged above the second layer 3 containing the soft magnetic fibers 4. As already previously described, the cellulose material 5 of the second layer contains only a diluted concentration of cellulose fibers. If now the still moist layer 3 is passed underneath the device 14, the soft magnetic fibers 4 have sufficient freedom of movement to orient themselves in the direction of an active magnetic field. The detection probability for the security elements 1 made from the material web 2, 3 can be considerably increased by the forced orientation of the magnetic fibers 4 in the predetermined concentration of soft magnetic fibers.

[0019] As already previously mentioned, the orientation of the soft magnetic fibers 4 can also be forced by mechanical action on the still moist cellulose material 5 containing the soft magnetic fibers 4. For example, a force component in the traveling direction of the web of material 3 can be simply achieved by accelerating the web of material 3 in the direction of travel.

[0020]FIG. 2 shows a perspective representation of a security element 1 manufactured by the method of the present invention. The security element 1 includes a first layer 2, being a cellulose material 6 composed of cellulose fibers without any further admixtures. The second layer 3 is composed of a mixture of a cellulose material 5 to which soft magnetic fibers are admixed. The length of the soft magnetic fibers 4 is calculated so that with great probability the fibers 4 will be excited in an electronic article surveillance system to emit a characteristic signal, as the result of which an alarm is activated.

[0021] According to a further aspect of the security elements 1 of the present invention, the soft magnetic fibers 4 are oriented essentially in one direction. This has the advantage of enabling the characteristic signal of the security element to be detected readily by an article surveillance system even with a small number of fibers 4 per security element 1.

[0022] The advantages of the security elements 1 produced by the method of the present invention are now reiterated by way of conclusion. By using two-ply paper for the production of the security elements 1 it is possible to maintain the concentration of cellulose fibers in the layer 3 containing the soft magnetic fibers 4 at a very low level. Consequently the concentration of soft magnetic fibers 4 can also be low, as the result of which the production costs for a security element 1 of the present invention can be minimized accordingly. A further advantage resides in the tear strength of the two-ply material web 2, 3. The layer 3 with the soft magnetic fibers 4 oriented essentially in longitudinal direction displays an anisotropic tear strength. The tear strength is very low particularly in the direction of orientation of the fibers 4. Considering, however, that Orientation of the cellulose fibers in the first layer 2 is completely arbitrary, the material web 2, 3 as such displays the preferred isotropic tear strength. Furthermore, it is possible to use very long fibers, and the fibers remain approximately stretched throughout the production process. List of References 1 security element of the invention 2 first layer 3 second layer 4 soft magnetic fiber 5 cellulose material for the second layer with soft magnetic elements 6 cellulose material for the first layer 7 hopper device 8 hopper device 9 surface supporting the cellulose material of the second layer 10 surface supporting the cellulose material of the first layer 11 guide roll 12 guide roll 13 pressure roll 14 guide roll 15 guide roll 16 guide roll 

1. A method of manufacturing security elements for electronic article surveillance, said method comprising the step of making the security elements of at least two layers, characterized in that a first layer (2) of a cellulose material (6) is applied in the still moist state to a second layer (3) of a cellulose material (5), with soft magnetic elements (4), which emit a characteristic signal in the interrogating field of an article surveillance system, being added to one of the two layers (2; 3), and in that the desired shape of the security elements (1) is die stamped or cut out of the two layers (2, 3) in the dry state.
 2. The method as claimed in claim 1, characterized in that in the moist state the soft magnetic elements (4) are oriented in essentially longitudinal direction of the material web (2; 3; 2, 3) by external force applied.
 3. The method as claimed in claim 2, characterized in that in the moist state the soft magnetic elements (4) are oriented in essentially longitudinal direction of the material web (2; 3; 2, 3) by a magnetic field acting in the longitudinal direction of the material web (2; 3; 2, 3).
 4. A security element for electronic article surveillance, manufactured according to the method of claim 1, characterized in that the first layer (2) is a cellulose material (6) comprised of cellulose fibers, and that the second layer (3) is a cellulose material (5) comprised of cellulose fibers in which soft magnetic elements (4) are contained which are excited in a magnetic interrogating field of an electronic article surveillance system to emit a characteristic signal.
 5. The security element as claimed in claim 4, characterized in that the magnetic elements (4) are fibers made of a soft magnetic material.
 6. The security element as claimed in claim 5, characterized in that the length of the soft magnetic fibers (4) exceeds 2 cm on average.
 7. The security element as claimed in claim 4, characterized in that the cellulose material (5) of the second layer (3) contains no more than half as many soft magnetic fibers (4) as cellulose fibers.
 8. The security element as claimed in claim 4, characterized in that the cellulose material (5) for producing the second layer (3) has a lower concentration of cellulose fibers than the cellulose material (6) of the first layer (2). 